The invention relates to a process for the preparation of carboxylated propylene polymers, to the carboxylated propylene polymers prepared and to their use.
It is known that by carboxylation of polypropylene it is possible to improve e.g. its dyeability and its adhesion to polar surfaces. The method commonly used to prepare such carboxylated polypropylene is grafting maleic anhydride onto commercially available polypropylene. This method however, requires a free-radical generating catalyst such as a peroxide. The presence of such compounds is known to lead to a severe reduction of the polymer molecular weight, thereby making the thus prepared carboxylated polypropylene unsuitable for those applications wherein the molecular weight of the polypropylene plays an important part.
U.S. Pat. No. 3,220,985 describes a process for modifying hydrocarbon polymers by reaction with monosulfonazide group-containing compounds, including m-carboxy benzene sulfonazide, under static conditions and in the absence of a free-radical generator. This process, however, has a disadvantage in that it is very slow and requires reaction times of 2-8 hours at 150.degree.-160.degree. C. Hence the problem underlying the present invention is developing a process for the preparation of carboxylated propylene polymers within a reasonable time and wherein the carboxylation does not simultaneously lead to a severe reduction in the molecular weight of the polymer.
EP 0086159 describes a process for crosslinking polymers and copolymers of .alpha.-olefins which is suitable for improving the mechanical resistance characteristics of said polymers under heat. This process can be accomplished within a relatively short time. It consists of grafting a carboxylic acid onto the polymeric chain through mechanical mixing thereof at a temperature of at least 170.degree. C., possibly in the presence of a generator of radicals, and the subsequent salification (neutralization to form a salt) of the free carboxylic groups with metal compounds of a basic character. However, this document does not teach how to avoid severe polymer degradation during carboxylation of the polymer.